Magnetic tape cartridges used in video cassette recorders include a pair of tape reels mounted in the cassette housing. Typically, these cassettes include a reel pressure spring mounted in a central portion of the upper housing of the cassette which places a downward force on the tape reels to maintain proper position and rotation of the tape reels. The spring is mounted at a central portion to the upper housing of the cassette and extends as arms which contact and bias the tape reels. Numerous reel spring configurations have been used.
Straight, planar springs with arms having parallel sides are disclosed in Carroll, U.S. Pat. No. 4,770,367. Schoettle, et al., U.S. Pat. No. 4,717,091, discloses a similar reel spring having a central mounting portion that projects out of the plane of the spring. U.S. Pat. No. 4,496,118 to Oishi, et al. discloses straight, planar springs having transversely extending central mounting protrusions. V-shaped, planar springs are shown in Ogata, et al., U.S. Pat. No. 4,449,676, and U-shaped, planar springs are shown in Goto, U.S. Pat. No. 4,504,028. In Carroll, Schoettle, et al., and Goto, the spring arms are uniformly wide. In Oishi et al. and Ogata et al., the spring arm width decreases toward the ends.
U.S. Pat. No. 4,662,579 to Gelardi discloses a diamond-shaped spring which uniformly narrows from a central mounting portion to the distal ends which can include a portion of constant width. The Gelardi spring uses strengthening ribs to enable the spring to be coined from metal having a thickness less than 0.30 mm (0.012 in). Maehara, U.S. Pat. No. 4,544,062, discloses a similar diamond-shaped spring in which the distal ends are wider than their immediately adjacent arms. Both springs include four sides, with two adjacent sides forming an arm, and a diagonal which transversely bisects the spring between the distal ends. Sato, et al., U.S. Pat. No. 4,593,868, is directed to an improvement of the diamond-shaped spring and discloses a Z-shaped spring formed by the diagonal and two sides of the diamond shape. The Z has the same general dimensions of the diamond; it has a central, maximum width, and the width decreases toward the distal ends. Like Maehara, the ends are wider than the immediately adjacent portion of the arm.
None of these reel springs is a linear spring in which the narrowest portion is the central portion between oppositely extending arms which widen toward their distal ends. Additionally, all of these reel springs use symmetric mounting holes formed on either the transverse central axis, the longitudinal central axis, or both. None of the known reel springs includes asymmetrical mounting holes which prevent the reel spring from being connected to the upper housing improperly.